1. Field of the Invention
The present invention relates to a hot crimping (thermal caulking structure) structure fixing a lens to a lens frame, and also relates to a hot crimping method of fixing a lens to a lens frame. The present invention further relates to a hot crimping tool for fixing a lens to a lens frame.
2. Description of the Related Art
A hot crimping method is often adopted to fix a lens (a lens element or a lens group) to a cylindrical lens frame made of synthetic resin. According to a conventional hot crimping method, a lens holder opening with a diameter corresponding to the diameter of the lens is formed on a lens frame, a stepped portion which is engaged with the rim of the lens is formed on an inner peripheral surface of the lens frame in the lens holder opening, and a thin-walled cylindrical portion is formed on the lens frame adjacent to the lens holder opening so that the lens is fixed to the lens frame by crimping the edge of the thin-walled cylindrical portion by heat in a direction radially inwards from the outside of the thin-walled cylindrical portion to bring the edge into intimate contact with an outer edge of the lens. The hot crimping tool (hot crimping horn) for this crimping operation is used in a manner to bring an inner conical surface, which is formed on an inner peripheral surface of the hot crimping tool, into contact with an outer peripheral surface of the thin-walled cylindrical portion.
Such a conventional hot crimping structure has been devised based on a technological common sense of preventing the hot crimping tool from contacting with any portion of the lens frame other than the thin-walled cylindrical portion. If the hot crimping tool accidentally contacts a portion other than the thin-walled cylindrical portion, there is a high possibility of the lens frame or a peripheral part thereof being unexpectedly deformed by heat.
The conventional hot crimping structure needs to be provided with not only the aforementioned thin-walled cylindrical portion but also a clearance recess for the hot crimping tool. This adds constraints to the shape of the lens frame, and increases the size of the lens frame. On the other hand, if the axis of the rotationally symmetrical hot crimping tool is not precisely coincident with the optical axis of the lens when brought into contact with the thin-walled cylindrical portion, the thin-walled cylindrical portion is not deformed uniformly. This may cause a poor crimping of the thin-walled cylindrical portion, so that the lens cannot be held properly by the lens frame.